According to the known method crankshaft pins are machined by lathing or rotary lathing with the crankshaft eccentrically mounted so as to produce a purely rotary movement about the crankpin axis. With this mounting machining of the cheeks is also possible but this type of machining has shown itself to be trouble-prone, in particular the chucks for eccentric mounting of the crankshaft are expensive. In addition the machining by lathing with a tool is done such that in a single operation a finished shape is produced that only needs in the region of the pin a finish machining by grinding. With this machining a different tool must be used for each different crank.
According to the method of the prior-art tool carriers are used with several cutting-insert types used on the tool carrier.
By means of this tool carrier the cheeks and undercuts to both sides of the shape and the entire length of the pin are finished in one cutting operation. Thus a tool carrier is needed for each finished shape.
According to a special goal of the method in a first step the cheeks are machined and in a second machining step the pins are machined to produce the pin diameter and the undercuts.
According to a second known method the crankshaft is clamped and machined with an inside miller that is moved in an orbit about the crank pin. Disadvantages of this machining are large movements and large moved masses so that high-speed machining is not possible.
A milling head for producing a bearing shape on a crank shaft in on step is known from German 3,824,348. The suggested milling head of the disk or collar type for machining crankshafts which have as surfaces to be machined by milling a cylindrical surface extending parallel to the milling-head axis and preferably merging via a rotation-symmetrical groove into a surface nearly perpendicular to the axis, with on the outside or inside cutter periphery of the milling head sets of indexable cutting plates secured in holders, is so constructed that several sets of indexable cutting plates are arranged uniformly around the cutter periphery of the milling head, that each set of indexable cutting plates fully covers the central shape of the surface of the workpiece to be machined and that at least one indexable cutting plate is provided inside one set of indexable cutting plates for each surface to be individually machined, and is so fitted with special indexable cutting plates that all the surfaces can be simultaneously machined.
A cutting insert to be called an indexable cutting plate which has a polygonal flat body with at least one main cutting edge, a cutting edge, and a free face, is known from German 4,400,570.
Also known is so-called high-speed milling, that is a metal-cutting machine with a miller (outside miller) that works
a) with a high cutting speed of more than 160 m/min, PA1 b) with a thin chip thickness in the region of 0.05 mm, preferably in the region of 0.05 mm to 0.1 mm, and PA1 c) with a reduced cutting-arc length. PA1 a) as a result of the considerable chip thickness and the relatively small engaging cutters at any time because of the very varied force distribution, considerable vibration is produced, PA1 b) the use of indexable cutting plates with negative cutting angle leads to high machining temperatures, PA1 c) the high machining speed produces such rapid tool wear that tight tolerances along the pin cannot be guaranteed, so that as a result the indexable cutting plates must be changed often which effectively negates the advantages of high-speed milling. PA1 1. The reduction in tool width caused by wear can easily be compensated for by moving the tool. PA1 2. As a result of the lightly angled indexable cutting plate (cutting insert) the finished shape has minimal offset errors. PA1 3. The cut width of the crank pin to be made is easily changed, that is according to setup the produced pin length can be changed with the same tool by about 5 mm. PA1 4. Loading of the machine and workpiece is maintained constant by the small unitary cutting width.
The term cutting-art length refers to the length of the tool carrier engaged with the corresponding cutting insert relative to its overall circumference.
High-speed milling produces such a good surface quality that pretreating or additional treatments before heat treatment as a separate step can be completely eliminated.
High-speed milling, although ideal because of its shortened machining time and better surface quality, is not used to date with the machining of cylindrical shapes, in particular crankshafts because with the known tools